It's very easy fix just loosen the round lock nut on the cable , where the throttle cable goes into the throttle grip assembly and turn the other round nut out a little until the slack is gone.
I believe the manual says something like 5-10mm which coincidentally 1/4" falls right into (6.35mm). The reason is that there is wiggle room so that the throttle won't open when you don't want it to. For example, if you turn your handlebars lock to lock, you may find that your throttle cable is routed such that it might be affected. Also, the heat from the engine and other things I think could affect it. Same with your clutch cable.